The oldest known legends that obviously relate to the Arthurian mythology are Welsh. But the further back you go, the less historical they become. And I don't

The oldest known legends that obviously relate to the Arthurian mythology are Welsh. But the further back you go, the less historical they become. And I don't mean in the sense of historical records being less reliable farther back in time; I mean that the characters in the oldest legends are clearly supernatural figures. There is no reason to postulate supernatural figures as having historical enemies. Why would they?